This invention relates generally to pumps which meter predetermined volumes and more particularly to such a pump employing a flexible liner.
Pumps are often used in applications where it is important to keep the surfaces contacting the fluent material being pumped clean. For instance, where the fluent material is a food additive for a food product, it is imperative that surfaces contacting the material be maintained in an aseptic condition. Accordingly, the parts of the pump which contact the food are made of materials (e.g., stainless steel) which are highly resistant to corrosion and can be cleaned. However, such materials are expensive and significantly increase the cost of the pump. The pump must be periodically shut down to clean surfaces which handle the food product. Cleaning may also involve continuing to operate the pump while flushing with a cleaning liquid. In any event, the pump is not available for production operation while cleaning is taking place. Many fluent food products are prone to leave residue or debris as they are handled, which cause the pump to become unsanitary. Although necessary, it is inefficient to stop the pump frequently for cleaning and this increases the cost of manufacturing the product.
Even when it is not necessary to maintain aseptic conditions, it frequently is important that a build up of the fluent material be avoided. As another example, a pump may be used in mixing paint. Operation of the pump can be hindered by a build up of paint in the pump. Moreover, color quality can be affected where paints are mixed by a build up of paint. Accordingly, it is necessary to clean the apparatus frequently.
Pumps used in situations like those described herein often are called upon to meter fluent materials in precise quantities. Such pumps also have application in the medical field for administration of, for instance, medicaments. It is known to use membrane pumps to administer precise quantities, particularly where small amounts of fluent material are metered. Membrane pumps typically have one or more cavities in a rigid base which are covered by a flexible membrane. A force can be applied, such as by fluid pressure, to the membrane to move it into the cavity to pump fluent material from the cavity. The fluent material still must come into contact with the rigid base in operation of the membrane pumps.